Question 75208
To find the greatest common factor between 2 numbers, we need to look for a number that can go into both 15 and 45. These numbers are:
1,3,5,15
Since 15 is the greatest of the list, it is the GCF. But we aren't done yet. There 's still an x term to be factored. The same idea applies as well. What factors do x and {{{x^2}}} share. They share a common term of x (they both have a term of x in them). So the GCF is:


15x


I can then factor out the GCF to get

{{{15x(1+3x)}}}

which is perfectly valid, since I can distribute to get 
{{{15x+45x^2}}}